1. Field of the Invention
The present invention relates to battery-powered cordless power tools. More specifically, the invention relates to a battery adapter system for a cordless power tool.
2. Description of Related Art
Cordless power tool systems including releasably attachable rechargeable battery units are widely known in the pertinent arts. Each portable power tool includes a housing that incorporates its own essential elements, such as an electric motor and a work element (e.g., reciprocating chuck for receiving a saw blade, rotatable chuck for receiving a drill bit, and the like), which are attached to the housing and driven by the motor. The motor, and therefore the work element, is powered by a portable rechargeable battery, or battery pack that is releasably attached to the housing of the power tool.
Various interfaces are known for electrically and physically coupling the battery or rechargeable battery pack in an electrical apparatus such as the housing of a power tool or a battery charger. In one known manner of operatively connecting a rechargeable battery to an electrical apparatus, a contact member of the rechargeable battery physically extends into the tool handle for engagement of associated electrical terminals. Such an arrangement is occasionally referred to as a plug-in type interface.
As used herein, the term “battery” will be understood to include a single rechargeable battery or a battery pack consisting of two or more batteries.
The useful time of a fully-charged battery will vary and will be shorter when the power tool requires a large amount of electrical power to perform its work. Such batteries can be considered relatively expensive in terms of the down-time required to recharge the battery, as well as the cost to either replace or purchase a separate back-up battery. Furthermore, the battery substantially increases the weight of the tool, resulting in user fatigue, since the majority of these power tools are designed to be hand-held.
In U.S. Pat. No. 5,076,805 to Welch, a handheld power tool is disclosed with an adapter that replaces the battery normally placed in the battery compartment of the device, where the adapter is capable of connecting to an external automotive battery. In U.S. Pat. No. 5,354,215 to Viracola, an interconnecting circuit element is placed in an internal battery compartment of the power tool which connects the power tool to a power source socket, such as a cigarette lighter socket of a vehicle. These devices are provided in order to extend the time that the tool can be used under the particular circumstances of accessibility to an alternative power source. However, hand tool battery output voltages vary among manufacturers and few, if any, correspond to the 12 volts of automotive batteries. Transformers would therefore be required to provide the correct voltage to the tool.
The approach exemplified by Welch and Viracola do ameliorate the disadvantages of batteries mentioned above, but they create other problems the use of batteries were meant to solve, namely, the lack of a conveniently available power source. Even though an automotive vehicle can be moved to many job sites, the user of a power tool is still limited to a semi-fixed electrical source, as envisioned by Welch or Viracola. Thus, the range that the user is able to use the power tool is limited by the length of the power cord connecting the Welch or Viracola tool to the automotive or other electrical outlet.
U.S. Pat. No. 4,988,584 to Shaper discloses that in order to supply electrical power from a rechargeable battery pack to a battery-powered flash unit, the individual batteries (e.g., four AA sized batteries) that normally power the flash unit are manually removed from a battery compartment provided in the unit, and a “power module” adapter is inserted into the compartment thereafter. A twin-conductor cable has one end connected to the power module adapter and an opposing end furnished with a connector. The connector is plugged into a rechargeable battery pack, thereby enabling electrical power to be provided from the battery pack to the flash unit.
Although the rechargeable battery pack in Shaper is described as being portable and capable of being carried by a person along with the flash unit, the portable battery pack is a separate device and is not truly interchangeable with the batteries normally inserted in the flash unit when the battery pack is not being utilized. Thus, the separate battery pack of Shaper is costly in terms of the additional expense of having to purchase the rechargeable battery pack. Furthermore, the batteries that are normally used to power the flash unit are different in size and shape from the rechargeable battery pack. That is, the battery pack is not an interchangeable plug-in battery for the flash unit. When the user of such an electronic flash unit removes the batteries normally used to power the device in order to insert the power module, the user must store them in a place that they will not get lost while they are not being used, as well as remember to replace them for the next time the flash unit is going to be used.
Therefore, there is a need in the art for an adapter capable of providing power to a portable power tool from a battery that is normally sold and used integrally with the power tool when the battery is removed to lighten the tool, as well as one that will enable the user to perform work tasks with the power tool without being restricted by the length of an attached extension power cord leading to an alternative power source.
As used herein, the terms “original battery” or “original equipment battery” means the battery sold by the tool manufacturer, or others, that are specially configured to mate with the tool, usually by insertion into the handle of the tool. Tradesmen commonly purchase at least two such rechargeable batteries so they can continue working while a battery is being charged.